Multiple channel zig-zag antenna array



Nov. 17, 1970 R. E. FISK MULTIPLE CHANNEL ZIG-ZAG ANTENNA ARRAY FiledDec. 16. 1968 FIGB /l6 INVENTORZ RONALD E. FISK,

BY ms ATTORNEY.

United States Patent "ice 3,541,564 MULTIPLE CHANNEL ZIG-ZAG ANTENNAARRAY Ronald E. Fisk, Syracuse, N.Y., assignor to General ElectricCompany, a corporation of New York Filed Dec. 16, 1968, Ser. No. 784,114Int. Cl. H01q 9/16, 19/10 US. Cl. 343-793 3 Claims ABSTRACT OF THEDISCLOSURE This invention relates to antennas, and more particularly toan antenna of the zig-zag panel type.

In many metropolitan areas, suitable locations for transmitting antennasare limited. Therefore, a means for using the existing space mostefficiently is highly desirable. A striking example of the lack ofavailability for suitable locations for transmitting antennas is that ofthe Empire State Building in New York City, where all televisiontransmitter antennas are concentrated. In other areas costly antennatowers must be built even though they are able to provide only limitedusable space for mounting antennas.

Accordingly, it is an object of this invention to provide an improvedantenna array comprising two zig-zag antennas occupying the physicalspace normally required for a single zig-zag antenna.

Another object of this invention is to provide an improved multiplechannel panel antenna array which comprises two zig-zag type antennasarranged in an extremely small spacial area.

Still another object of the present invention is to provide twointerleaved zig-zag type antenna radiators which are arranged on acommon panel and disposed in parallel spaced apart planes.

Further objects and advantages of my invention will become apparent asthe following description proceeds.

Briefly, in carrying out one form of my invention, there is provided aninterleaved zig-zag antenna array which comprises a generallyrectangular, planar, electrically conductive reflector upon which ismounted in spaced insulated relationship an outer zig-zag radiator andan inner zig-zag radiator interleaved between the outer radiator and thereflector. The outer radiator transmits on a first operating channelfrequency and the inner radiator transmits on a second, higher operatingchannel frequency. Each radiator is spaced from the reflector a distanceequal to between one-tenth and fifteen onehundredths of the wave lengthat the mean operating frequency of that particular radiator. Thus theouter radiator, transmitting at a mean operating frequency lower thanthat of the interleaved inner radiator, will be spaced at a greaterdistance from the reflector than the inner radiator. Each radiator iscomprised of a like number of zig-zag elements of a length L equal toonehalf wave length'at the mean operating frequency of the respectiveradiator. Because the operating frequency of the outer radiator is lowerthan that of the inner radiator, the length L of the elements of theouter radiator is greater than that of the elements of the innerradiator. The corresponding elements of the outer and inner radiatorscross near the respective midpoints at approximately 90 in order tominimize the coupling effect between Patented Nov. 17, 1970 theradiators. Therefore, the pitch angle of the elements of the outerradiator is approximately the complement of the pitch angle of the innerradiator. By this invention, an antenna array is provided which occupiesno greater space than did previous single zig-zag panel antennas, whilealso producing improved multi-channel broadcast capabilities.

The novel features believed characteristic of this invention are setforth in the appended claims. The invention itself, together withfurther objects and advantages thereof, may best be understood byreference to the following description, when taken in conjunction withthe accompanying drawing, in which:

FIG. 1 is a front elevation view of a multiple channel zig-zag typeantenna array embodying my invention in one form thereof;

F161. 2 is a side elevation view of the antenna array of FIG.

FIG. 3 is a section view taken on lines 33 of FIG. 1;

FIG. 4 is a front elevation view of a modified form of the antenna arrayof FIG. 1.

Referring to FIGS. 1-3 of the drawings, it will be seen that there isprovided a zig-zag type panel antenna array comprising a generallyrectangular, planar, electrically conductive reflector 6, and outer andinner zigzag radiators 8 and 10, respectively, spaced apart andinsulated from the reflector 6 by a plurality of standoff insulators,exemplified by the insulators designated with reference numeral 12. Theradiators 8 and 10, are each disposed in a separate plane, their planesof disposition being in parallel spaced apart relationship to each otherand to reflector 6.

The outer radiator 8 comprises a number of zig-zag conductor elements 14connected in seriatum, each element being joined to the next successiveelement at a predetermined angle, one-half of which angle is defined asthe pitch angle A of the element. The pitch angle A of each element 14(as shown in FIG. 1), may also be defined as the angle the element makeswith a plane perpendicular to the longitudinal axis of the radiator 8.

Each zig-zag element 14 of the radiator 8 as measured from a corner toan adjacent corner has a nominal length L equal to one-half wavelengthat the mean operating frequency f of the channel upon which the radiator8 is operating. The radiator 8 is fed at a medial feed point 16 througha coaxial cable 18 delivering an RF voltage at operating frequency fRadiator 8 is spaced from the reflector 6 by a predetermined criticaldistance. Optimum performance of the radiator 8 has been found to obtainwhen the radiator 8 is spaced from the reflector 6 a distance within therange of one-tenth to fifteen one-hundredths wavelength at the operatingfrequency f of the radiator 8.

The inner radiator 10 is interleaved between the outer radiator 8 andthe reflector 6 and is essentially like the outer radiator 8, beingcomprised of a plurality of zig- Zag conductor elements 20 with a pitchangle B and a length L, equal to one-half wavelength at the meanoperating frequency f of the channel upon which the radiator 10 isbroadcasting. The radiator 10 is fed at medial feed point 22 through acoaxial cable 24 delivering an RF voltage at operating frequency f Theinner radiator 10 is also spaced from the reflector a distance withinthe range of one-tenth to fifteen one-hundredths wavelength at itsoperating frequency f The inner radiator 10 transmits at a higheroperating frequency than the outer radiator '8, that is, f is greaterthan f Since both radiators -8, 10 are spaced from the reflector 6 thesame distance, in terms of wavelengths at the respective operatingfrequencies, the inner radiator 10' will be located closer to thereflector 6 than the outer radiator 8 which transmits at a longerwavelength.

It is of crucial importance that the outer and inner radiators 8, 10 beisolated from each other, viz, the mutual coupling between the radiatorsmust be reduced to inconsequential proportions. If substantial couplingis present between the radiators 8, 10, the radiation from one radiatorwill be picked up by the other radiator and reflected back through thefeed line of the latter to and from its transmitter, producing aghosting effect at the television receiver which picks up the signal.Other problems may be engendered by excessive coupling between theradiators, such as the generation of intermodulation components in thetransmitter of the coupled radiator which would be broadcast from thecoupled radiator in the form of spurious outerband radiation.

The desired degree of isolation between the radiators 8, 10 is achievedin accordance with the present invention by aligning the radiators 8,-10 such that the element 14 of the outer radiator 8 crosses over thecorresponding elements 20 of the inner radiator 10 at their respectivemidpoints and at approximately 90. It is evident that because the innerradiator 10 is transmitting at a shorter Wavelength than the outerdariator 8, the half-wavelength elements 20 of the inner radiator 10will be shorter than the corresponding elements 14 of the outer radiator8. Thus, in order for corresponding elements 14, 20 of the outer andinner radiators 8, -10 to cross at their midpoints at approximately 90,the pitch angle A of the outer radiator 8 must be less than 45 and thepitch angle B of the inner radiator 10 must be greater than 45. In fact,a trigonometric analysis will show that if the corresponding elements ofthe outer and inner radiators cross at exactly 90, then the sum of thepitch angle A of the outer radiator 8 and the pitch angle B of the innerradiator 10 will be equal to 90. Thus for large differences in theoperating frequencies f f of the outer and inner radiators 8, 10 thepitch angle A of the elements 14 of the outer radiator 8 will approachwhereas the pitch angle B of the inner radiator will approach 90. Itwill be understood then from the above discussion that isolation betweenthe outer and inner radiators 8, 10 can be achieved regardless of theoperating frequencies of the radiators or the operating frequencydifference between them.

A modified form of my invention is illustrated in FIG. 4. Thismodification of the basic antenna array is designed to achieve evengreater isolation between the outer and inner radiators 8', 10' than ispossible with the embodiment of FIGS. 1-3. This is accomplished bylongitudinally shifting the position of one radiator along the axis ofthe panel with respect to the other radiator. In this arrangement thenon-overlapping end portion of each of the radiators 'will broadcastwith almost a total absence of coupling with the other radiator. Thistechnique can be utilized where a slightly greater vertical space isavailable for mounting an array than is occupied by the embodiment ofFIGS. 1-3 wherein the radiators are completely coextensive.

This invention is not limited to the particular details of theconstruction of the embodiment illustrated and I contemplate thatvarious and other modifications and applications will occur to thoseskilled in the art. It is therefore my intention that the appendedclaims shall cover such modifications and applications as do not departfrom the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A multiple channel zig-zag panel antenna array comprising:

(a) an electrically conductive reflector,

(b) a first zig-zag radiator comprising a plurality of zig zag elementsand being mounted in insulated spaced relationship to said relflector,said first radiator being fed from a first source of RF voltage at afirst operating frequency, and

(c) a second zig-zag radiator interleaved between said first radiatorand said reflector, said second radiator comprising a plurality ofzig-zag elements and being mounted in insulated spaced relationship tosaid reflector, said second radiator being fed from a second source ofRF voltage at a second operating frequency,

((1) said first radiator elements and said second radiator elementscrossing at approximately to minimize coupling between said first andsecond radiators.

2. A multi-frequency zig-zag panel antenna array comprising:

(a) an electrically conductive planar reflector,

(b) a first zig-zag radiator fed from a first source of RF voltage at afirst operating frequency, said first radiator being spaced tenhundredths to fifteen hundredths wavelength at said first operatingfrequency from said reflector and insulated therefrom, and said firstradiator comprising a plurality of zig-zag elements, said elementshaving a length equal to onehalf wavelength at said first operatingfrequency and a pitch angle A, and

(c) a second zig-zag radiator fed from a second source of RF voltage ata second operating frequency, said second radiator being spaced tenhundredths to fifteen hundredths wavelength at said second operatingfrequency from said reflector and insulated therefrom, and secondradiator comprising a plurality of zig-zag elements, said elementshaving a length equal to onehalf wavelength at said second operatingfrequency and a pitch angle B, said second operating frequency beinggreater than said first operating frequency,

(d) said first radiator elements and said second radiator elementscrossing near their respective midpoints, and the sum of said pitchangles A and B equaling approximately 90.

3. The antenna array defined in claim 2 wherein said first and secondradiators are axially offset with all except an end portion of each ofsaid first and second radiators in overlapping relationship.

References Cited UNITED STATES PATENTS 3,369,246 2/1968 Fisk et al.343-806 3,375,525 3/1968 Fisk et al 343806 X 3,409,893 11/1968 Siukola343-806 X HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, AssistantExaminer US. Cl. X.R. 343-797, 806, 834

